1. Field of the Invention
The present invention relates to a medium conveying device that conveys a sheet-like medium, and an image recording apparatus using the medium conveying device.
2. Description of the Related Art
When a sheet used for printing is in a high-humidity environment, the sheet includes moisture and is deformed. Further, since a portion, to which ink has been applied, of a sheet having been subjected to printing is lengthened, the sheet having been subjected to printing is also deformed. This deformation of the sheet is referred to as curl or cockle.
When the deformed sheet is conveyed by a drum or a belt and is subjected to printing by an ink jet method, a slow distance (the flight distance of an ink droplet) is changed. For this reason, there is a problem that the quality of an image to be printed may deteriorate. Further, there is also a problem that the sheet may come into contact with a print head and may cause a trouble.
In order to solve these problems, in the related art, a sheet conveyed by a drum or a belt has been made to be even by a roller so that the deformation of the sheet is removed.
However, the amount of deformation of the sheet is not constant and a variation is usually present at each position in one sheet. When the sheet having a variation in the amount of deformation is made to be even uniformly by a roller, there is no position to which a large amount of original deformation of the sheet escapes. For this reason, finally, there is a problem that wrinkles and floating may be generated.
For example, in the case of a sheet which a high-density image is recorded at both end portions thereof in a width direction, the deformation of both the end portions of the sheet is greater than that of the middle portion of the sheet. Accordingly, when the sheet is made to be even uniformly by a roller, there is no position to which deformation generated at both the end portions escapes. For this reason, since deformation is concentrated on the middle portion of the sheet, there is a problem that wrinkles and floating may be generated at the middle portion.
In order to solve this problem, JP2012-24990A discloses a technique for suppressing the generation of wrinkles and floating by forming stepped portions, which further protrude than a middle portion, at both end portions of a drum in a width direction.
Further, JP2013-151149A and JP2000-191175A disclose techniques for absorbing the deformation of a sheet by recessed portions to suppress the generation of wrinkles and floating by forming recessed portions and protruding portions on the peripheral surface, which is a sheet holding surface, of a drum or a belt.